In the production of a separator for a battery with improved stability, dip coating is one of the methods of applying a solid coating to a web. Dip coating refers to a method that coats a slurry (coating solution) to a web by passing the web through the slurry held in a dipping bath, with the web traveling along a guide roll placed in the dipping bath.
The slurry coated to the web goes through a drying oven installed outside of the bath, drying a solvent included in the slurry and therefore leaving only solids and an adhesive coated to the web.
Meanwhile, a slurry includes about 80% of a solvent and the remaining 20% of solids and an adhesive, and due to the solids having a higher density than the solvent, a precipitation phenomena in solids may occur at a bottom surface of a bath during a reaction.
Referring to FIG. 1, a slurry flows into a bath 1 through an inlet 2 connected to a side surface of the bath, circulates through the bath, and flows out to a circulation tank through an outlet 3 connected to a bottom surface.
However, since this bath structure has an inherent drawback of reducing in a flow rate of the slurry in an area near the bottom surface, it is difficult to overcome the precipitation phenomena in solids occurring at the bottom surface. When an amount of precipitation increases, a coating process must be stopped and an operation of removing the precipitation must be performed, causing a reduction in productivity and a failure to achieve a desired coating property due to the solids being thrown away.
Accordingly, there is an urgent need for a solution to increase a flow rate of a slurry at a bottom surface of a bath to a maximum as well as allowing a uniform distribution of the slurry in the bath.